1. Field of the Invention
The present invention is related to temperature sensing techniques and devices and, more particularly, is directed towards a method and apparatus for fluidically sensing the surface temperature of an object without contacting same.
2. Description of the Prior Art
In the present age of dwindling material energy resources, special emphasis has been placed by our national leaders on conservation--conservation of raw materials and reduction of energy usage per given process. It is therefore important to determine those processes that use or require the most energy. It is also critical to provide for the optimum use of the energy available.
To this end, it is interesting to note that studies conducted by the government and industry have indicated that in high-temperature processes where vast quantities of fuels, and hence energy, are used, the normal mode of operation is one of overcompensation. Products are overheated to ensure that they are at least at the minimum working temperature because no reliable temperature sensors, or no sensors at all, are available to establish the correct temperature. Precise knowledge of the process temperature at all stages would increase speed of working because less reheating and less handling would be necessary. Less reheating or, more precisely, less time at temperature would result in major energy savings. Current estimates indicate that simply monitoring temperature at critical process points may reduce total energy consumption by about 10 percent. If automatic temperature control can be incorporated into high-temperature processes it would obviously further reduce energy consumption and have the added benefit of a simplified and shorter production cycle.
Considerable effort has been expended on devising sensing techniques appropriate for military/industrial processes. The result in the current off-the-shelf state of the art is the development of various electronic and electro-optical transducers. Thermocouples and resistance thermometers are the old standbys; optical or infrared (IR) sensors are the new devices available. Disadvantages of these devices are that thermocouples alloy, diffuse, oxidize, or melt; resistance thermometers oxidize or melt. Both must be protected and thus often suffer from inadequate transient response. Optical sensors require clear optical paths, a good knowledge of the material emissivity, and heavy protection if the transducer itself is located near the process. Optical spectroscopy becomes unmanageable because of time restraints, actual physical bulk, and cost. At very high temperatures, above 1200.degree. C. (2200.degree. F.), only optical techniques have shown acceptably reliable operation, despite their limitations.
In the past 17 years, fluidic technology has addressed temperature measurement. A fluidic edgetone oscillator as described in U.S. Pat. No. 3,706,227 to Gottron et al was built out of graphite and operated at over 4000.degree. F. (2200.degree. C.). Not much was done with this device because of an oxidation problem. More recently, the Garrett-AiResearch Corportion has installed a fluidic sonic-oscillator temperature sensor in its automotive gas turbines. This sensor has proven continuous operation up to 1050.degree. C. (1900.degree. F.). It is constructed of high temperature steel. ERDA has recently become interested in monitoring the extremely high temperatures in foundry and other high energy consuming processes such as glass manufacture, so in conjunction with U.S. Army efforts relating to high-temperature monitoring in its own processes (rocket exhausts, tank and gun barrel forging, and gas turbine control), an effort in fluidic high-temperature sensing was initiated. Fluidics was chosen because it appeared to be the only technology that has only one limitation; that is, the temperature to be measured must be less than the melting temperature of the sensor. In addition, the simplicity of a fluidic sensor/preamplifier results in very low initial costs, and extremely long operating life.
The present invention is an outgrowth of the above-described research effort.